There is widely known a displaying apparatus mounted on a head to view an image, that is, a head mounted display (HMD). The head mounted display has an optical unit for each of right and left eyes and is configured to be able to control the senses of sight and hearing when it is used with headphones. When it is configured so as to be completely cut off from the outside world at the time it is attached to the head, the virtual reality is increased at the time of looking and listening. Also, the head mounted display can reflect different images to right and left eyes, and, when images with disparity are displayed to the right and left eyes, it is possible to present a 3D image.
As display units for the right and left eyes on the head mounted display, it is possible to use a display panel of high resolution including, for example, a liquid crystal and an organic EL (Electro-Luminescence) device. Also, if an adequate angle of view in an optical system is set and the multichannel is realized by headphones, it is possible to realize the sense of presence similar to looking and listening in a movie theater.
It is known in the industry that if the display panel constituted by the liquid crystal, the organic EL device, or the like continues to display high luminance images, a burn-in phenomenon becomes likely to occur. Therefore, in the head mounted display, a display control method that achieves a long life of a display device by adjusting the luminance has been desired.
In the imaging technique field, there is widely known a technology that adjusts the luminance of a display screen depending on the illumination intensity (environmental light) in an installation environment of a displaying apparatus such as a television receiver or a projector, that is, in a viewing environment.
For example, there is proposed an image displaying apparatus that follows a change in feature quantity of input image signals and changes the dimming speed of the backlight source, based on the difference in the times necessary for the light adaptation and the dark adaptation (for example, see Patent Literature 1).
Also, there is proposed an image displaying apparatus that acquires the luminous environment in the surroundings using an illumination intensity sensor, and switches an image setting suitable for the surrounding environment without giving an audience a feeling of strangeness (for example, see Patent Literature 2).
Also, there is proposed an image displaying apparatus that sequentially calculates an image quality correction amount corresponding to a display luminance level, and thereby, even if the image luminance is controlled, allows a watcher not to feel that the image quality or visibility is degraded, based on the dark adaptation to brightness feeling of human eyes and time (for example, see Patent Literature 3).
However, either of the above-described conventional technologies does not intend to perform an adjustment of luminance for a head mounted display. In a displaying apparatus that directly covers eyes, such as a head mounted display with a light shielding feature, the viewer is in the same environment as being in a dark place. Therefore, after mounting the head mounted display, the dark adaptation occurs in the eyes of the viewer as a luminosity property. Furthermore, when mounting the head mounted display with a light shielding feature, the eyes of the viewer are shielded from environmental light, and therefore it makes no sense to measure the illumination intensity in the viewing environment.